Trunk circuits for automatic telephone systems



July 28, 1925.

A. B. SMITH TRUNK CIRCUITS FOR AUTOMATIC TELEPHONE SYSTEMS Filed Sept.18, 1919 Fm &

Imuenfur firzhur" EEEEEyFmZIh Patented July 28, 1925.

entree ARTHUR BESSEY SMITH, OF EVANSTGN, ILLINOIS, ASSIGNOR 'IOAUTOMATIC E LEO- TRIC COMPANY, O'F CHICAGO, ILLINOIS, A CORPORATION OFIIlLIlfl'QIS.

TRUNK CIRCUITS FOR AUTOMATIC TELEPHONE SYSTEMS.

Application filed September To all whom it may concern Be it known thatl, ARTHUR. Bnssnx SMITH, a citizen of the United States of America, anda resident of Evanston, in the county of Cook and State of Illinois,have invented certain new and useful Improvements in Trunk Circuits forAutomatic Telephone Systems, of which the following is a specification.

My invention relates in general to auto matic trunk circuits, but moreparticularly to trunk circuits connecting more or less isolated orseparated automatic exchanges, and has for its primary object theprovision of means for handling a special case having-to do with thecollection of tolls on incoming calls, although certain broad featuresmay be found to be of utility for other purposes.

Fig. 1 is a layout of the relative position of a group of exchanges inwhich my invention may be best illustrated.

Fig. 2 is a diagram of the selective switching mechanism which is usedto illustrate the features of my invention.

Referring to Fig. 1 of the drawings, the reference characters A, B, andC represent three exchanges which may be located in three difierenttowns. Vi e will assume that the towns in which exchanges B and C arelocated are relatively close together, or these exchanges may be in thesame town or city. At any rate, they are so situated that a fiat ratefor calling is in force for inter-exchange as well as local calls.Exchange A however, is somewhatmore distant and while calls fromexchange A to exchange B may carry no extra charge, there will be a tollcharge for calls from exchange A to exchange C. lnter exchange as.wellas local calls are established automatically by the subscribersexcept that an operator may complete those calls which carry an extratoll charge. The trunking may be described briefly as follows: Atexchange A selector switches are provided as usual which are common tothe subscribers and which are used during a preliminary stage in allconnections, local or inter-exchange. Thus the selector S has access tolocal trunks and also to trunks extending to exchange B, one of which isshown in the drawing. This-trunk line terminates at exchange B in aselector S which may be termed a trunk selector to distinguish it fromthe local selector S which is similar to selector S at eXchange A. Se

18, 1919. Serial No. 324,284.

lectors S and S have access in common to local trunks in exchange B andto interexchange trunks extending to exchange C. It will be seen nowthat subscribers in both exchanges haveaccess to trunk lines extendingto exchange G. Since there is no extra charge for calls betweenexchanges B and C such calls are preferably established auto-v.matically, and to this end each trunk line is provided with a branch atexchange Cwhich terminates in an automatic switch. But there is a chargefor calls from exchange A to exchange 0 which makes it necessary toroute such calls thru an operator who can make appropriate recordthereof. In order to take care of this latter class of calls a sec ondbranch is provided for each trunk line which extends to an operatorsposition. Heferring again to the drawing'it will be seen that the trunkextending from exchange B to exchange C terminates at the latter pointin a switching device X which is adapted to connect. the trunk line tothe branch extending to jack J, or to the branch extending to the switchS The object of my invention is, specifically, the provision ofautomatic means at exchange C which is able to differentiate betweencalls from exchange A and calls from exchange B, and which is effectiveto dire-ct calls from exchange A to an operator and calls from exchan eB to automatic switches thru the medium of which the subscriberscomplete the desired'connections The precise manner in which this isaccomplished and the preferred embodiment of the invention. will bedescribed more in detail hereinafter, reference being had to theaccompanying drawing.

In the drawing (Fig. 2), the reference,

characters and 31 indicate the two line conductors of one of the trunklines connecting exchanges B and C. This trunk line terminates atexchange 13 in the repeating coil It thru the medium of which the trunkconductors are inductively connected to con-' ductors 8 and 9. Theselatter conductors terminate in multiple contact sets in the banks oflocal selectors such asselectors S Fig. 1, and also extendto multiplecontact sets in the banks of trunk selector 'such as the. selector S,Fig. 1. In the drawing here is shown one contact set, comprisingcontacts2, 3, and 4, which is located in the bank of a local selector; andanother contact set comprising contacts 5, 6, and 7 which is located inthe bank of a trunk selector. It is understood that while the linecontacts are multipled between the local and trunk selectors, theprivate or test contacts are not so multipled. Thus the test contact 3is multipled to other local selectors but not to trunk selectors whilesimilarly test contact 6 is multipled only to other trunk selectors.

At exchange C the repeating coil R is provided thru the medium of whichthe trunk conductors 30 and 31 are inductively connected to conductors32 and 33, which are normally connected to branch conductors 44 and 45extending to jack J. The other branch comprises conductors 42 and 43which extend to a selector switch which may be the selector S Fig. 1.This latter branch is normally disconnected but may be substituted forthe other branch by the operation of relay 37.

It is thought that the operation and functions of the various relays canbest be explained by describing the operations incident to theestablishment of several representative connections over the trunkcircuit. Accordingly it will be assumed first that a calling subscriberin exchange B has estab' lished connection thru the medium of theselector S with the bank contacts 2, 3, and 4 for the purpose ofconnecting via the trunk circuit with a subscriber in exchange C. Uponthe completion. of the connection to the bank contacts 2, 3, and 4, theline relay 13 is energizedin the usual manner over the callingsubscribers loop and upon attracting its armature 15 closes anenergizing circuit for the slow acting relay 14. This latter relay pullsup and closes the well known holding circuit back to the selector Swhich extends from ground G by way of armature 16 and its workingcontact, winding of relay 20, and conductor 10 to bank contact 3, whenceit continues by way of the test wiper of the switch thru a relay whosefunction it is to maintain the switch in operated position, and thenceto the ungrounded pole of the battery. Current flow in the holdingcircuit serves to energize relay 20, which upon energizing, completes acontrol circuit over the trunk line to exchange C as follows; ground atG thru the battery 13, working contact of armature 22 and the saidarmature, armature 18 and its working contact, working contact ofarmature 17 and the said armature, conductor 19, right hand windings ofrepeating coil R in parallel, trunk conductors 30 and 31 in parallel,left hand windings of repeating coil R in parallel, conductor 51, andwindings of polarizedrelays 46 and 47 in series to ground G Upon thecompletion of the above circuit the direction of lay 47 is able tooperate its armature, but polarized relay 46 remains inoperative. Relay47 upon operating, com" pletesa circuit for the relay 36 which in turncloses acircuit for the slow acting relay 37. This relay, uponenergizing, dis

connects the conductors 32 and 33 from branch conductors 44 and 45 atarmatures 40 and 41, respectively, and connects them instead tothebranch conductors 42 and 43 which extend to a selector switch, assumedto be the selector S Fig. 1. Relay 36 has already closed at its armature39 a normally open contact in conductor 42 and it Will be seen thatrelays 36 and 37 have now completed a loop circuit including the righthand windings of repeating coil R :and which extends to the line relayof the selector. V

Controlling impulses for operating the selector switch and subsequentswitches, in exchange C are transmitted over the trunk line in thefollowing manner: Then the subscriber at exchange; Boperates his callingdevice a series of interruptions are produced in the line circuit,thereby causing a corresponding series. of deenergizations of line relay13. At each deenergization relay 13 breaks the control circuit extendingto current flow is such that polarized re- 1 exchange "C, therebycausing the polarized relay 47 t0 deenergize a like number of times.Since relay 47 controls the circuit of relay 36, this relay alsodeenergizes a plurality of times and thereby produces a series ofinterruptions in the circuit which extends over the branch conductors 42and 43 to the selector switch. Subsequent op-' erations of the callingdevice by the subscriber at exchange B will result in the operation ofan additional switch or switches in exchange G whereby the connectionwill be completed to the desired line, all in the well known manner.

Having described. briefly the establishment of aconnection between asubscriber in. exchange B and one in exchange G, I will now describe theoperation when a subscriber in exchange A is calling. It will be assumedthat the calling subscriber desires to obtain connection with asubscriber in exchange C and that he has extended his line through themedium of selectors S and S to the trunk line terminal comprising bankcontacts 5, 6, and 7. Upon the completion of the connection, line relay13 is energized, followed by the energization of relay 14, which relaycloses the holding circuit back to the selector S the same as wasdescribed in the case of selector S except that now the relay 21 isincluded instead of relay 2() Upon energizing, relay 21 connects thebattery B in the control circuit extending over the two conductors ofthe trunk in parallel to exchange C, where it includes the polarizedrelays 46 and 47. Batteries B and B have'different poles adapted forconnection to the control circuit, or inother words, they have oppositev and will thereafter proceed as is usual in such cases, making properrecord of the call, and then completing it to the called line in anysuitable manner.

The foregoing explanation is believed to be sufficient to enable theinvention to be readily understood. It will be seen that I have deviseda trunk circuit connectingtwo exchanges and accessible at one end to twodifferent classes of subscribers, and having means at the other endwhereby calls from ill one class of subscribers are automatically routedto an operator, and whereby calls from the other class of subscribersare automatically routed via automatic switches.

lVhat I claim as my invention is:

1. In a telephone system, a trunk line, two classes of subscribershaving access to said trunk line when calling, two outgoing branches ofsaid trunk line, automatic selective means for routing calls from saidtrunk line via either of said branches, a pair of relays constitutingsaid selective means, a. controlling circuit for said relays, a pair ofbatteries each adapted to operate a particular one of said relays, andmeans controlled according to the class of a calling subscriber forconnecting one or the other of said batteries in said circuit.

2. In a telephone system, an exchange comprising an operators positionand a plurality of automatic switches, subscribers lines grouped at twooutside points, means whereby subscribers in both groups can call saidexchange automatically, and automatic means controlled by currents ofdifferent character for selectively switching such calls independent ofcontrol by the subscribers, whereby calls from one group of subscribersare directed to the operator and calls from the other group are directedto automatic switches.

3. In a telephone system, a trunk line having two branches at one endthereof, subscribers lines grouped at two points, means wherebysubscribers in both groups can connect with said trunk at the endopposite said branches and extend calls thereover, and automatic meanscontrolled over two sides of said trunk line in parallel for selectivelyswitching such calls independent of control by the subscribers, wherebycalls from onev group of subscribers are extended over one branch ofsaid trunk line and calls from the other group'are extended over theotherbranch.

4. In a telephone system, a trunk line, branches of said trunk line atone end there of, one branch extending to,- an operators position andthe other branch terminating in an automatic switch, two selectorswitches having access to said trunk at the opposite end thereof, andmeans for always signalling the operator'via one of said branches whenthe trunk is seized by a particular. one of said selectors and foralways operating said automatic switch when the trunk is seized by theother ofsaid selectors, said means controlled by currents of differentcharacter.

I 5. In a telephone system, a trunk line having two branches at one endthereof and a simplex circuit superimposed thereon, one branch beingnormally connected and extending to an operators position and the otherbranch being normally disconnected and terminating in an automaticswitch, two selector switches having access to said trunk at theundivided end thereof, and automatic means controlled over saidsuperimposed circuit for completing the connection to the operator viathe said connected branch whenever the trunk is seized by a particularone of said selectors, and for connecting the said normally disconnectedbranch and for disconnecting the other branch whenever the trunk line isseized by the other of said selectors.

6. I n a telephone system, a trunk line having two branches at one endthereof, two selector switches having access to said trunk at the otherend, a circuit superimposed on the conductors of said trunk line andincluding at the divided end of the trunk two relays for controllingextensions of said trunk over its two branches, respectively, twoseparate batteries at the o her end of said trunk for separatelyoperating said relays, and means whereby each of said selectors when itseizes the trunk line includes a particular one of said batteries in thesaid circuit.

7. In a telephone system, a trunk line having two branches at one endthereof, two selector switches having access to said trunk at the otherend, a ground return circuit superimposed on the conductors of saidtrunk line, two polarized relays included in said circuit at the dividedend of said trunk for controlling the connection of said trunk .vith itstwo branches, respectively, two batteries at the other end of said trunkhaving opposite poles grounded, and means whereby each of said selectorswhen it seizes the a particular one of said relays.

e .8. In a telephone system, an exchange comprising an operatorsposition and a plurality of automatic switches, second and thirdexchanges each having subscribers" lines terminating therein, a trunkline accessible to subscribers lines in the second exchange andextending to said third exchange, another trunk line accessible to callscoming over said first trunk and also to subscribers in said thirdexchange, the said second trunk constituting means whereby subscribersin either the said second or third exchanges can call the said firstexchange,

and automatic means for selectively switching such calls independent ofcontrol by the subscribers whereby calls from the second exchangeraredirected to an operator and whereby calls from the third exchange aredirected to automatic switches.

9. In a telephone system, two classes of lines, a trunk, means forconnecting any line with said trunk at the incoming end thereof, twobranches of said trunk at the outgoing end, discriminating mechanism at,the incoming end of said trunk sensitive to the class to which aconnected line belongs, and switching mechanism at the distant endcontrolled over a talking conductor of said trunk by said discriminatingmechanism for routing all calls from lines of one class via one of saidbranches and all calls from lines of the otherclass via the other ofsaid branches.

10. In a telephone system, a trunk line having two branches at theincoming end, an automatic selector switch having access to the firstbranch only, a second automatic selcctor'switch having access to thesecond branch only, two branches at the outgoing end of said trunk line,means including said selectors for extending calls over said trunk line,and cooperating means atopposite ends of said trunk line for insuringthat all calls reaching the trunk line by way of one selector will berouted away from said trunk line via a particular branch at the distantend and that all calls arriving by way of the other selector will berouted via the other branch at the distant end. a e

11. In a telephone system, a trunk line having two branches at one endthereof, automatic switching inechanismfor connecting a calling linewith said trunk line at the other end, a circuit including the twotalking conductors of said trunk line in parallel, and switching meansat the junction of said branches controlled automatically over saidcircuit responsive to the establishment of said connection for routingthe call over a particular one of said branches. i

12. In a telephone system, a trunk line having two branches at theincoming end and two corresponding branches at the outgoing end,automatic switches torextending calls over said trunk line, a circuitincluding the two talking conductors ofsaid trunk line in parallel, andmechanism at the outgoing end of said trunk line controlled over saidcircuit from the incomingend for automatically and selectively switchingsaid calls, said mechanism including means for routing eachcall awayfrom the trunltover the outgoing branch corresponding to the incomingbranch inuse.

Signed at Chicago, Cook County, Illinois, this 13th day of September,1919.

ARTHUR BESSEY SMITH.

